Because of the random bursts of blistering heat known as Daybreak nothing could survive on it's surface. But the northern half of the planet eventually became covered with these Vines and other life soon followed.
Only the Northern third of the planet is known to harbor life, the rest remains too cold due to it's northern surface always pointing towards the Core and the rest of the planet facing empty space. The lower 2/3rds is known as the Unclaimed.
Sanctum drags it's northern hemisphere against the Veil closest to their star as it circles the Core of the universe. It slowly sinks into the Veil until hit by a Daybreak, Pending on where it is on it's revolution and the time since it's last Daybreak it can break free of the Veil for a short time before reforming into what is known as the umbilical.